1. Field of the Invention
This invention relates to high-boiling hydrochlorofluorocarbon (HCFC) solvents and a novel method of using the same in cleaning applications. More specifically, the invention relates to admixtures of hydrochlorofluorocarbons and selected organic solvents that exhibit a vapor pressure significantly lower than predicted by Raoult's law for ideal mixtures and their use at elevated temperature in liquid/vapor phase cleaning applications.
2. Description of the Related Art
It is generally known that during the manufacture of machinery parts, household utensils, tools, electronic components, and many other products, one of the more important steps is the cleaning of the finished parts. Oil, grease, contaminants from soldering processes such as flux residues, solid buffing compounds adhering to the manufactured items, and the like must be removed before sale or use. Modern electronic instruments and control devices, for example, require cleanliness of their parts to an unprecedented degree.
For convenience and effectiveness, removal of contaminants from manufactured items, particularly metal items, is done by rinsing in an organic solvent. Generally the cleaning process involves immersing the item to be cleaned in a solvent, often a heated solvent, for a period of time, followed by immersion in a clean solvent or in the vapor of the clean solvent. The cleaning solvent may contain additives such as detergents to enhance the cleaning action of the solvent.
Hydrocarbon solvents have been and are being used in cleaning processes because of their effectiveness in removing oil and grease residues and their low cost. However hydrocarbon solvents are generally very flammable, often incompatible with polymeric substrates, and are often toxic. Chlorinated hydrocarbon solvents have been used to reduce flammability, but in general they are more toxic than the hydrocarbon solvents. Chlorofluorocarbons, such as for example, 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113), because of their greatly reduced toxicity and their non-flammability, have found acceptance as good organic solvents for the many cleaning processes. Popularity of CFC-113 as the cleaning solvent is due to its many desirable characteristics in addition to the above-mentioned non-flammability and greatly reduced toxicity, such as convenient and useful boiling point of about 48.degree. C., which allows enhanced cleaning at a convenient operating temperature and easy purification and recovery for recycle, its compatibility with most organic polymeric materials and metals, its solvency characteristics, and its very high degree of inertness, i.e. stability.
However, in recent years, the outstanding stability of the fully halogenated chlorofluorocarbons (CFCs), which includes CFC-113, has been cited as contributing to their role in the depletion of the stratospheric ozone layer. It has been suggested that the stability of the CFCs is such that, when released into the atmosphere, ultimately some will reach the stratosphere unchanged and by ultra-violet-promoted decomposition may participate in the ozone-depletion process. Consequently, it is now generally recognized that there is a need to develop alternatives to CFCs which have no or very little effect upon the ozone-depletion process.